Session 2: MPLS Traffic Engineering and Constraint-Based Routing (CR)

Transcription

1 MPLS Frame Relay Alliance formed in April 2003 Session 2: MPLS Traffic Engineering and Constraint-Based Routing (CR) Copyright 2003 MPLS Frame Relay Alliance Slide 2-12 MPLS Routing h The need for Traffic Engineering extensions Constraint-based Routing (CR) h OSPF Traffic Engineering (OSPF-TE) TE link characteristics OSPF-TE LSA (Link State Advertisements) h IS-IS Traffic Engineering (ISIS-TE) in comparison with OSPF-TE Slide 2-22

2 MPLS Routing h The need for Traffic Engineering extensions Constraint-based Routing (CR) h OSPF Traffic Engineering (OSPF-TE) TE link characteristics OSPF-TE LSA (Link State Advertisements) h IS-IS Traffic Engineering (ISIS-TE) in comparison with OSPF-TE Slide 2-32 Limitations of Current IGP Control Mechanisms h Interior Gateway Protocol (IGP) control capabilities are not adequate for Traffic Engineering (TE) h IGPs based on shortest path algorithms significantly contribute to congestion problems in Autonomous Systems (AS) within the Internet protocols are topology driven Shortest Path First (SPF) algorithms generally optimize based on a simple additive metric bandwidth availability and traffic characteristics are not considered in routing decisions Slide 2-42

3 Open Shortest Path First (OSPF) h OSPFv2 Interior Gateway Protocol (IGP) link-state protocol neighbour discovery and maintenance Link State Advertisements (LSA) 0 link-state database 0 link state database distribution (reliable flooding) routing calculations 0 Dijkstra s Shortest Path First (SPF) algorithm h TE extensions extended link attributes extended database Slide 2-52 Constraint-based Routing Operational Model 1) Routing table OSPF-TE ISIS-TE 2) TE Database (TED) Operations performed by the I-LER 1) Store information from IGP flooding in a routing table 2) Store Traffic Engineering Information in a TED OSPF and IS-IS - TE extensions Distributed (piggybacked) on Opaque Link State Advertisements (LSA) Encoded as new "Type-Length-Values" (TLV) objects New parameters: TE metric (e.g., delay, loss, cost), max BW, max reservable BW, unreserved BW, administrative group ("color") Slide 2-62

4 Constraint-based Routing Operational Model OSPF-TE ISIS-TE Operations performed by the I-LER 1) Routing table 2) TE Database (TED) 4) Constr SPF 3) User constraints 1) Store information from IGP flooding 2) Store Traffic Engineering Information 3) Examine user defined constraints 4) Calculate the physical path for the LSP 5) Represent path as an explicit route 6) Pass ER to RSVP-TE for signaling 5) Expl route 6) Signaling Slide 2-72 Constraint-based Routing I-LER E-LER User-defined LSP constraints h h LSP constraints are configured at the Ingress LER bandwidth requirement inclusion or exclusion of specific links Inclusion of specific nodes traversal QoS and/or CoS parameters Control mechanisms select an LSP path that meets the constraints Slide 2-82

5 MPLS Routing h The need for Traffic Engineering extensions Constraint-based Routing (CR) h OSPF Traffic Engineering (OSPF-TE) TE link characteristics OSPF-TE LSA (Link State Advertisements) h IS-IS Traffic Engineering (ISIS-TE) in comparison with OSPF-TE Slide 2-92 OSPF-TE h TE-enabling link characteristics traffic engineering metric, e.g.: delay, delay variation, loss maximum bandwidth, i.e.: nominal bandwidth of a link maximum reservable bandwidth; allows to specify: over-provisioning over-subscription unreserved bandwidth for each of eight classes resource class/color a bit mask that determines to which class(es) a link belongs (e.g., satellite link, link that can be used only by selected users, link with special pricing) Slide 2-102

6 TE Link Characteristics Traffic Engineering Metric Traffic Engineering metric h Traffic Engineering metric link metric (e.g., delay, delay variation) may be different than the standard OSPF link metric Slide TE Link Characteristics Bandwidth bandwidth Traffic Engineering metric h Bandwidth: true link capacity units: bytes per second Slide 2-122

7 TE Link Characteristics Reservable Bandwidth Over-subscription Over-provisioning bandwidth Traffic Engineering metric Reservable Bandwidth h Reservable Bandwidth: user configurable units = bytes per sec = max BW default < max BW over-provisioning > max BW over-subscription Slide TE Link Characteristics Unreserved Bandwidth Over-subscription Over-provisioning Unreserved bandwidth bandwidth Traffic Engineering metric Reservable Bandwidth Reserved Bandwidth h Unreserved Bandwidth bandwidth not yet reserved at each of 8 priority levels initial values = Reservable Bandwidth Slide 2-142

8 TE Link Characteristics Resource Class/Color Over-subscription Over-provisioning Unreserved bandwidth bandwidth Traffic Engineering metric Reservable Bandwidth Resource class/color Reserved Bandwidth h Resource Class/Color administrative group membership per link bit mask Slide Opaque LSA Format for OSPF-TE Standard LSA Header Advertising Router Link 1... Link n LSA Payload 32-bit word aligned application-specific coded as TLVs, I.e., Type- Length-Value triplets Slide 2-162

9 OSPF-TE Opaque LSA Header 0 31 LS Age Options Type = 10 LSA Header for TE Advertising Router LSA ID = 1 Instance Advertising Router LS sequence number LS checksum Length Link 1... Link n h Opaque LSA link-state type defines flooding scope: Type = 10 area-local (type-9 is link-local type-11 is AS) h LSA ID = 1 (TE) Instance arbitrary value used to maintain multiple TE LSAs Slide OSPF-TE Opaque LSA Payload LSA Header Advertising Router TLV Link 1 TLV... Link n TLv h Type h 1 = router address (single TLV) h 2 = link (nested TLVs) h Length = number octets in the Value portion h Value h depends on the type h 32-bit aligned h padding is not included in the Length count h nested TLVs: Value is a set of sub-tlvs Slide 2-182

10 OSPF-TE Opaque LSA - Link sub-tlvs Link sub-tlvs Link type (point-to-point or multi-access) Link ID (in pt-to-pt router ID of a neighbor) Local interface IP address (1 to N local addr) Remote interface IP address (1 to N rem addr) Traffic engineering metric bandwidth reservable bandwidth Unreserved bandwidth Administrative group ("resource class/color") Type Length 1 octet 4 octets 4N octets 4N octets 4 octets 4 octets 4 octets 32 octets 4 octets Slide MPLS Routing h The need for Traffic Engineering extensions Constraint-based Routing (CR) h OSPF Traffic Engineering (OSPF-TE) TE link characteristics OSPF-TE LSA (Link State Advertisements) h IS-IS Traffic Engineering (ISIS-TE) in comparison with OSPF-TE Slide

11 ISIS-TE vs. OSPF-TE TE Extension OSPF ISIS Traffic Engineering metric bandwidth reservable bandwidth Unreserved bandwidth Resource class/color Slide Path Computation Using Estimated Bandwidth for Best Effort Traffic BEFORE 30% 50% 60% AFTER ADDING 10Mbps 70% 60% 62.5% SELECTED PATH 70% 30% San Jose 50% 60% Washington 62.5% 60% Slide

12 MPLS Routing Summary h Traffic Engineering extensions for OSPF and IS-IS provide routers a dynamic and more exact view on network capacity, load, congestion state, and other link attributes enable Constraint-based Routing (CR) through intelligent path computation/explicit route determination, and therefore MPLS Traffic Engineering Slide IGP-TE References h OSPF-TE references: Traffic Engineering Extensions to OSPF version 3, draft-ietfospf-ospfv3-traffic-00.txt, April 2003 Traffic Engineering Extensions to OSPF version 2, draft-katzyeung-ospf-traffic-09.txt, October 2002 h IS-IS-TE reference: IS-IS extensions for Traffic Engineering, draft-ietf-isis-traffic- 04.txt, December 2002 Slide

13 MPLS Frame Relay Alliance formed in April 2003 End of Session 2 Thank You Copyright 2003 MPLS Frame Relay Alliance Slide